Robot intelligence in natural environments

ABSTRACT

A method for automatic, decentralized coordination of the movement paths of mobile robots in order to prevent collisions and to detect and resolve mutual blockings. According to the method, a robot receives position information from other robots and establishes a coordinating connection with another robot if the position falls below a minimum allowable distance. One of the robots is then chosen as coordinator and the other robot is chosen as partner. The coordinator initiates an algorithm for the prevention of collisions, wherein a time sequence diagram is determined for the motion path segments of the coordinator and the partner. A robot for detecting robots that are mutually blocking one another in a circuit initiates an algorithm for detecting blocking if the robot has not been given authorization to execute its next motion path segment. An algorithm for resolving the blocking is initiated if robots mutually blocking each other in a circuit are detected by the detecting robot. The algorithm includes a first step and optionally a second step, whereby the sequence for the execution of the next motion path segment of the robots is interchanged during a coordinating connection and the motion paths of one or more robots mutually blocking each other in a circuit are newly planned.

This is a Continuation of International Application PCT/DE02/01174, withan international filing date of Apr. 2, 2002, which was published underPCT Article 21(2) in German, and the disclosure of which is incorporatedinto this application by reference.

FIELD OF AND BACKGROUND OF THE INVENTION

The present invention is directed to coordination of the independentmotion paths of robots in a working environment used by these robots. Inparticular it relates to a method of automatic, decentralizedcoordination of the independent motion paths which can be broken downinto segments of a plurality of mobile robots communicating with eachother within a specified geographical area, to avoid collisions and todetect and resolve mutual blocking.

When a number of mobile robots share the same working environmentaccount must be taken of the fact that the robots might collide witheach other. The danger of a collision generally increases with thenumber of robots used. To avoid collisions, the motion paths of theindividual robots must be coordinated.

Methods of avoiding collisions between robots, in general, are known.

A method in which it is possible to dispense with a communicationsnetwork between the robots provides for the introduction of trafficrules for example by which collisions are avoided if the rules areobserved by all robots. The disadvantage of this method is however thatvery specific assumptions must then be made about the workingenvironment. This type of method is described, e.g., in S. Kato, s.Nishiyama and J. Takeno “Coordinating Mobile Robots by Applying TrafficRules”, International Conference on Intelligent Robots and Systems(IRQS), pp. 1535-1541, 1992.

In another method in which a communications network between the robotscan also be dispensed with, the robots are equipped with sensors whichcan detect other robots within a specific area. Whenever a robot detectsanother robot the point at which the robots might possibly collide iscomputed and the motion path is modified accordingly to avoid acollision. Since however the motion paths are replanned on a local basisthis can result in mutual blockings of the robots (see below) which willnot be detected and resolved. This method is described for example in L.Chun, Z. Zhang and W. Chang, A Decentralized Approach to theConflict-Free Motion Planning for Multiple Mobile Robots, “Int. Conf. onRobotics and Automation (ICRA), pp. 1544-1549, 1999.

Another approach follows procedures in which the motion paths arecoordinated by means of a central component. There are basically twooptions available here, one of which simultaneously creates the centralcomponents for collision-free motion paths for all robots involved; theother makes it possible for independently planned motion paths of therobots only to be coordinated subsequently by using the centralcomponents. The first method is described for example in J. Barraquand,B. Langlois and J.-C. Latombe “Numerical Potential Field Techniques forRobot Path Planning, IEEE Trans. On System, Man and Cybernetics, Vol.22(2), pp. 224-241, 1992. An example of the second method can be foundin S. Leroy, J. P. Laumond and T. Simeon “Multiple Path Coordination forMobile Robots: A Geometric Algorithm”, International Joint Conference onArtificial Intelligence (IJCAI), 1999, and M. Bennewitz and W. Burgard,“Coordinating the Motions of Multiple Mobile Robots Using a ProbalisticModel”, 8th International Symposium on Intelligent Robotic Systems(SIRS), 2000.

The disadvantage of all these methods which use a central component forcoordinating the motion paths is however that they need a globalcommunications network between the robots. Over and above this thesemethods are computation-intensive and inflexible.

An easier and more adaptable coordination between the robots with a lessexpensive communications network could be achieved by decentralizedalgorithms in which there is communication only between pairs ofphysically adjacent robots.

OBJECTS OF THE INVENTION

An object of the present invention is thus to specify a method fordecentralized coordination of the motion paths of a plurality of mobilerobots communicating with each other within a specified geographicalarea. Another related object is to provide such a method that avoidscollisions as well as detects and resolves mutual blocking. Yet anotherobject is to avoid the disadvantages and thereby improve upon theconventional methods.

SUMMARY OF THE INVENTION

These and other objects are achieved by the features of the independentclaims of the present invention. Advantageous exemplary embodiments ofthe invention are specified in the dependent claims.

In accordance with one formulation of the invention, a method ofautomatic, decentralized coordination of the independent motion pathswhich can be broken down into segments of a plurality of mobile robotscommunicating with each other within a specified geographical area, toavoid collisions and to detect and resolve mutual blocking is specified.In the method:

a robot receives positioning information from the other robots anddetermines its distance (d_(rob)) to the other robots,

when a robot moves to within a specified distance (d_(safe)) of theother robots it sets up and maintains a coordination connection to theserobots to coordinate its motion path with the motion paths of the otherrobots for as long as is at less than the prespecified relativedistance, in which case one of the robots linked by the coordinationconnection is selected as coordinator and the other as partner,

a coordinator requests the planned movement segments of its partner andinitiates an algorithm for avoiding collisions by which the motion pathsegments of the partner are harmonized with its own motion path segmentsin order to determine the collision areas in which the robots are lessthat a specified minimum distance (d_(90 min)) apart and in which atiming sequence scheme for the motion path segments of coordinator andpartner is determined,

on the basis of the timing sequence scheme for the motion path segmentsof coordinator and partner, a coordinator gives permission to itself andits partner to execute the next motion path segment and the motion pathsegment is only executed when the permission is granted,

a robot initiates an algorithm to detect blocking in order to detect agroup of mutually blocking robots if it has not been granted permissionto execute its next motion path segment,

on detection a group of mutually blocking robots by the detecting robotan algorithm to resolve the blocking is initiated comprising a firststep and a second step, with the first step being that with acoordinating connection of the mutually blocking robots the sequence forexecuting the next motion path segment is exchanged between the robotsconnected by a coordination connection in each case and with the secondstep being that one or more of the robots belonging to a group ofmutually blocking robots plan new motion paths, with the second steponly being executed if the first step has not led to the blocking beingresolved.

This process will now be explained in greater detail. In the method inaccordance with the invention each robot is capable of communicatingwith all other robots and of exchanging information about the relevantlocation if the other robots are within a specific prespecified distanceof it. Each robot evaluates the location information received from theother robots and determines the physical distance between itself and theother robots (any imprecision between the distance calculated from thelocation information provided by the other robots and the actualdistance between the two robots should in any event be less than δd.)

When a robot determines that its distance from another robot, designatedas d_(rob), is less than a prespecified minimum distance designated asd_(safe), minus the possible margin for error δd, d_(rob)−δd<d_(safe)this robot initiates a coordination connection to the other robot. Thiscoordination connection is maintained for as long as the two robots areless than a prespecified minimum distance apart. Each robot can In thiscase simultaneously initiate and maintain a number of coordinationconnections to other robots, if it is not at the prespecified minimumdistance d_(safe) from these robots.

The object of a coordination connection between two robots is tocoordinate the motion of two robots along their motion paths in such asway that collisions between them are avoided. In practical terms in thiscase each motion path of a robot is broken down into a sequence ofsegments.

Between two robots linked by a coordination connection one will beselected as coordinator and the other as partner in each case. After oneof the robots has been defined as coordinator it requests from itspartner the segments of its motion path and reconciles these motion pathsegments with its own motion path segments. If matching time-spacemotion path segments of coordinator and partner are found these motionpath segments are evaluated as colliding. From this information thecoordinator determines a timing sequence scheme for the motion pathsegments of the motion paths of coordinator and partner. From this pointon the coordinator grants itself and its partner the relevant permissionto execute the next motion path segment of their motion path. Withoutsuch permission the next motion path segment of a motion path may not beexecuted. In this case permission to execute the next motion pathsegment is granted either to only the coordinator, or only the partner,or to both. A lack of permission for the next motion path segment thuscorresponds to a wait time imposed on the robot.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail, by way ofexample, with reference to the embodiments depicted in the figures, inwhich:

FIG. 1 shows an example of a task completion diagram;

FIG. 2 shows a graphical representation of coordination connectionsbetween robots;

FIG. 3 shows a task completion diagram in which execution precedence isinterchangeable;

FIG. 4 shows an example of a blocked group of robots;

FIGS. 5A and 5B are representations, by way of example, of environmentsin which the inventive method is suitable to be implemented;

FIGS. 6A and 6B are graphs showing coordination connections versusnumber of robots for the environments of FIGS. 5A and 5B, respectively;

FIGS. 7A and 7B are graphs showing the number of blockings versus thenumber of robots for the environments of FIGS. 5A and 5B, respectively;and

FIGS. 8A and 8B are graphs showing the average motion path lengthsversus the number of robots for the environments of FIGS. 5A and 5B,respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An advantageous embodiment of the invention provides for the timingsequence scheme for the segments of the motion paths of coordinator andpartner to be determined by an algorithm based on the work of K. Kantand S. W. Zucker, “Toward Efficient Trajectory Planning: The PathVelocity Decomposition”, The International Journal of Robotics Research,Vol. 5, pp. 72-89, 1989 and P. A. O'Donnell and T. Lozano-Periz,“Deadlock-Free and Collision-Free Coordination of Two robotManipulators; Int. Conf. on Robotics and Automation (ICRA), pp. 484-489,1998. Both of these articles are incorporated into the presentapplication by reference.

In this case the motion path segments of a coordinator and itscorresponding partner are initially made available in a two-dimensionaldiagram (Task Completion Diagram) with the motion path segment of thecoordinator and of its partner being represented by the horizontal andvertical axis of the diagram in each case. A typical such diagram isshown in FIG. 1 The values of the motion path segments will be shown asconstant, regardless of the actual execution time of the segments. Thestart point of the two motion paths is in the bottom left corner of thediagram, the end point of the motion paths is in the top right corner.

The colliding areas are determined by checking whether a specificsegment of the coordinator and a specific segment of the partner lead toa collision, i.e. whether there are two positions of the robots in thesegment which produce a distance between the robot which is less than aprespecified minimum distance d90 min. This type of collision checkingmust be undertaken for all combinations of the coordinator and partnersegments. All colliding areas for which the collision checking hasproved positive are marked. In FIG. 1 all colliding areas arehighlighted in black.

After completion of the diagram an execution path is determined avoidingall marked, colliding areas, beginning with the bottom left corner andending in the top right corner. Advantageously the shortest executionpath is selected from what is generally a plurality of possibleexecution paths since this path causes the smallest total delay for therobot. In determining the execution path the differing execution timesof the motion path segment should also have been taken intoconsideration.

Finally the execution path is used to determine the sequence scheme forexecuting the motion path segment of coordinator and partner. Startingfrom the bottom left corner, the path is broken down into equal sectionswith an entry being made in the sequence scheme for each section. Foreach horizontal section an entry is made signifying that the coordinatorhas permission to take this path; for each vertical section an entry ismade signifying that the partner has permission to take this path; andfor each diagonal section an entry is made signifying that both robotshave permission to take this path; If permission is now granted to onlyone of the robots to execute its next motion path segment this meansthat the other robot must wait until it has executed its motion pathsegment. This corresponds to insertion of wait times into the motionpath segment of the waiting robot.

If no execution path can be determined, i.e. there is no possibleexecution path, a special entry is added to the sequence scheme whichspecifies that no robot is given permission to execute the next segment.

Each robot can be connected to a number of other robots, both ascoordinator and as partner, by a coordination connection. This resultsin coordination of a number of robots in a global coordinationstructure. Each robot must therefore have the permission of allcoordination connections linked to it before it may execute its nextmotion path segment. In this case a situation can occur in which anumber of robots have to wait for each other before they may executetheir next motion path segment so that the robots are mutually blockingone another in the execution of their motion path segment. Suchblockings (deadlocks) must be detected and rectified to enable therobots to continue to be used.

Since a mutual blocking can only occur when a robot must wait untilanother robot has executed its motion path segment, it initiates ablocking detection when it is forced to wait for another robot.

The coordination connections between the robots can be provided with adirection, graphically symbolized by a direction arrow, in order toindicate that a robot must wait for another robot until the latter hasexecuted its motion segment. This type of symbolic representation isshown in FIG. 2. The nodes of the diagram correspond to the robots, thearrows connecting the robots symbolize the coordination connection, withthe robot to which the tip of the arrow points having precedence for theexecution of its motion path segment over the other robot from which thearrow originates. For example robot 9 must wait for robot 0 until thelatter has executed its motion path segment. Robot 4 and 6 are mutuallyblocking each other since both must wait for each other until the otherrobot has executed its motion path segment. Robots 1, 2 and 3 are alsomutually blocking each other. As can be seen from FIG. 2 a detection ofmutual blockings can be reduced to locating closed groups along thedirectional coordination connections.

Preferably an algorithm is used for this which is based on the work ofK. M. Chandy, J. Misra and L. M. Hass, “Distributed Deadlock Detection”,ACM Trans. On Computer Systems, May 1983. This article is incorporatedinto the present application by reference as well. In this case for thecreation of a direction for a coordination connection from the robotfrom which the direction arrow originates, a test message is initiatedand is sent along the directed coordination connection. This testmessage is forwarded by all robots that receive it by their directedcoordination connection. In this case an identification of each robotthat has passed on the test message is flagged in the test message. Whena robot finally receives a test message which it has initiated itself, ablocking is detected. The blocking can be notified immediately using theflagged identifications of the robots passed.

With this algorithm it can occur that more than one robot detects thesame blocking, e.g. when two robots initiate blocking detection for thesame closed group at the same time. This is of no importance howeversince the solution for such blockings in accordance with the inventioncan also handle multiple detections of the same blockings. Equally itcan occur that apparent blockings are detected, i.e. blockings that havealready been resolved. This can occur for example when a directedcoordination connection belongs to two different blockings and thisdirected coordination connection has already been changed within thecontext of the resolution of the other group of mutually blockingrobots. The algorithm in accordance with the invention for resolvingblockings can however also handle apparent blockings.

If a mutual blocking of robots is detected a blocking resolution isinitiated by the robot detecting it.

A resolution of a mutual blocking of robots comprises two steps, wherebythe second step is only executed if the first step has not beensuccessful.

The first step consists of reversing the direction of a directedcoordination connection in the closed group of mutually blocking robots.Since this means that the group is no longer closed, mutual blocking isresolved. As has already been shown, the direction of a directedcoordination connection specifies which robot has precedence forexecution of its next motion path segment. However situations can occurin which it is not a matter of which of the two robots has precedence inmoving first but merely that the two robots do not move at the sametime. FIG. 3 shows a typical example of such a situation. With thecollision area highlighted in black in FIG. 3 first the coordinator andthen its partner can be moved to bypass it (solid line). Alternativelyhowever the partner can be moved first and then the coordinator (dashedline). What is more, in the example shown there is no significantdifference discernable in the total execution time of the two robots. Ina task completion diagram a collision area in which it does not matterwhether the coordinator or its partner is moved first can be found bythe execution path determined meeting a collision area at its leftbottom corner.

In order to now determine whether a directed coordination connectionexists for which the direction can be reversed a change message ispreferably sent around the closed group by the robot detecting theblocking. When a robot receives a change message it asks the coordinatorof the directed coordination connection going out from it which belongsto the group whether the direction of the directed coordinationconnection can be changed. If the coordinator is in a position to createan alternative sequence scheme for executing the motion path segment inwhich for bypassing a collision area it does not matter whether thecoordinator or its partner is moved first, the direction of the directedcoordination connection is reversed. In addition the change message isdiscarded. The resolution of the mutual blocking of the robots and thealgorithm to resolve the blockings is ended. If the direction of adirected coordination connection of a closed group cannot be reversed inthis way the second step of the algorithm in accordance with theinvention for resolving the mutual blocking of robots is performed.

The second step for resolving blockings consists of one or more robotsof a blocking planning alternative motion paths. The situation in whichall robots plan new motion paths at the same time should be avoidedhere. Rather, as with the algorithm shown here, as few robots aspossible should plan a new motion path.

Planning new motion paths preferably comprises two steps which areperformed iteratively until the blocking is resolved or until it isdecided that the blocking cannot be resolved when only individual robotsare requested to change their motion paths. The latter situation isregarded as highly unlikely in actual practice and only depends on thecharacteristics of the unit planning the motion path and thecharacteristics of the environment.

The first step includes sending a new planning message to the closedgroup of blocking robots, using the same procedure as used to send thechange message. When a robot receives a new planning message it asks itsmotion path planning unit whether an alternative motion path can beplanned. In this case the robot can inform its motion path planning unitabout the positions of the surrounding robots, i.e. the robots to whichthere are coordination connections, in order to achieve better results.When a robot is able to plan an alternative motion path all outgoingdirected coordination connections are removed. Since this interrupts theclosed group, the blocking is thus resolved. The new planning message isthen discarded. When a robot receives a new planning message which wasinitiated by itself however, it can be deduced from this that no robotin the group was capable of planning an alternate motion path.

When a blocking could not be resolved during the first step then it canbe that it is temporarily not possible to do so. This case can arise forexample if other robots in the neighborhood of a robot are preventing itfrom creating a new motion path. These two cases can be distinguished bythe following criterion:

When none of the robots involved is capable of planning an alternatemotion path and if none of the robots involved has an uninvolved robotin its neighborhood, the blocking cannot be resolved by requestingindividual robots to plan alternate motion paths.

A robot will be regarded as involved in this case if it is part of thegroup or if it is assigned to the group by an outgoing coordinationconnection either directly or transitively FIG. 4 shows a typicalblocked group of robots 1, 2 and 3 as well as a number of involvedrobots.

The idea of the second step for planning and alternate motion path isnow to check this criterion and ask robots involved which are not partof the group whether they can plan alternate motion paths. This enablesas many blocked robots as possible to be freed.

During the second step for planning an alternate motion path a freeingmessage is preferably sent to all robots involved. This occurs on theone hand when the freeing message is sent around the group and on theother hand by enabling the freeing message to leave the group and tocross to the robots involved using coordination connections going tothem. In this case those robots which have already received the freeingmessage are left out. FIG. 4 illustrates the path of the freeing messageinitiated by robot 2, with the broken arrows indicating the direction ofthe group and the black solid arrows the path during the crossing over.

The freeing message is used to ask the robots which are not part of thegroup whether alternate motion paths can be planned and to collectinformation as to whether non-involved robots are still in theneighborhood. When a robot receives a freeing message which it hasinitiated itself it knows that all the robots involved have received themessage. The robot then evaluates the criterion presented above and endsthe blocking resolution when the conditions for it are fulfilled.

Should the highly unlikely event occur that no direction of a directedcoordination connection can be reversed and that none of the robotsinvolved can change its motion path all robots involved in a blockinggroup are informed about this. These robots then no longer take part ina procedure to detect and resolve the blocking group.

FIGS. 5 to 8 will now be used to illustrate an exemplary embodiment ofthe method in accordance with the invention.

To this end the method in accordance with the invention has beenimplemented with the preferred algorithms used and tested in thesimulation. As a test model two different environments are assumed,namely a supermarket with just one area and a series of shelves, as wellas an office-like environment consisting of a plurality of areas linkedto each other by a corridor with individual obstacles. This is in shownin FIG. 5, whereby FIG. 5A shows the supermarket and FIG. 5B the office.The environments were 10×15 m in size.

The robots used for the simulation were 1 m high and 0.8 m wide and weremoved at a speed of 0.3 m/s. FIG. 5 shows 5 robots in the differentenvironments in each case.

For each environment 6 simulation runs each with from 1 to 6 robots wereperformed. Each of the 12 simulation runs lasted for 10 min. During thesimulations the robots followed randomly planned motion paths. Toevaluate the simulation runs the average number of coordinationconnections for a robot, the number of blockings occurring and theaverage motion path length of the robots after each simulation run weredetermined.

FIG. 6 shows the average number of coordination connections of a robot,with FIG. 6A showing the result for the supermarket and FIG. 6A theresult for the office. As can be seen from FIG. 6, the average number ofcoordination connections increases almost linearly with the number ofrobots. The reason for this lies in the fact that the average number ofcoordination connections depends on the number of robots in theneighborhood of a robot and this has a linear dependence on the numberof robots used.

FIG. 7 shows the number of mutual blockings of the robots. In their turnFIG. 7A shows this number for the case of the supermarket and FIG. 7Bfor the case of the office. It increases significantly when more thanfour robots are used. As can be seen from FIG. 7, in the case of two tothree robots the amount of collisions in the office is two to threetimes greater than in the supermarket. The reason for this lies in thefact that the office features a “hot spot”, namely the corridorconnecting the individual rooms. This is used regularly by the robots.The influence of the corridor however declines as the number of robotsincreases because the probability of collisions in the individual roomsincreases with increasing numbers.

Almost all blockings must have been resolved by planning new motionpaths; only 3% of blockings could be resolved by simply reversing thedirection of a directed coordination connection.

Finally FIG. 8 shows the average motion path length of the robots. FIG.8A again describes the case of the supermarket and FIG. 8B that of anoffice. Since a robot moves at a speed of 0.3 m/s and a simulation runsfor 10 minutes, a robot can move a distance of 180 meters in the bestcase. The actual values are however less than this since the robots mustwait for one another and become involved in mutual blockings which mustbe resolved. As can be seen from FIG. 8, the average motion path lengthfalls significantly when more than four robots are used.

It is evident from this simulation that the method in accordance withthe invention is able to coordinate the robots, avoiding collisions anddetecting and resolving blockings. The necessity to detect and resolveblockings significantly increases with the number of robots used. Ifmore than four robots are used in the environment considered, theperformance of the method drops markedly, as can be seen from theaverage length of movement paths.

In summary it can be established that with the method in accordance withthe invention there is decentrailized coordination of the independentmotion paths of a plurality of mobile robots to avoid of collisions anddetect and resolve blocking groups.

This basically occurs by a combination of three algorithms whichreliably resolve the problem defined. These do not use any globalsynchronization, do not interact with each other and need only localcommunication between the robots. A global coordination of a set ofrobots is achieved in that more than one coordination connection ispossible to each robot. This networks a set of robots into a globalstructure.

Mutual blocking in the global coordination which cannot be avoided ifonly local coordination is used, will be reliably detected. The mutualblockings are resolved by reversing the direction of the coordinationconnections and asking robots to change their motion paths. Theindividual mutual blockings which cannot be resolved are those for whichthe units of the robots concerned planning the motion paths are not in aposition to create alternate motion paths. This however only depends onthe skills of the unit planning the motion path of the robot and thecharacteristics of the environment.

The strict separation of the planning of motion paths on the one handand collision avoidance/handling of mutual blocking on the other handallows the units planing the motion paths to use it entirelydifferently. The only restriction lies in that fact that these must be aposition to plan alternate motion paths.

Naturally the invention is not restricted to the movement of mobilerobots. Mobile robots in the sense of the invention can also be mobileparts of robots, for example robotic arms.

An advantageous application of the method in accordance with theinvention lies in the coordination of the independent motion paths of aset of mobile robots for joint cleaning of a large area, e.g. a largesupermarket, a warehouse or an airport.

The above description of the preferred embodiments has been given by wayof example. From the disclosure given, those skilled in the art will notonly understand the present invention and its attendant advantages, butwill also find apparent various changes and modifications to thestructures and methods disclosed. It is sought, therefore, to cover allsuch changes and modifications as fall within the spirit and scope ofthe invention, as defined by the appended claims, and equivalentsthereof.

1. A method for automatic, decentralized coordination of independentmotion paths that are broken down into motion path segments of aplurality of mobile robots communicating with each other within aspecified geographical area, to avoid collisions and to detect andresolve mutual blockings, comprising: a robot receiving positioninginformation from the other robots and determining its distance (d_(rob))to the other robots, when the robot moves to within a specified relativedistance (d_(safe)) of at least one of the other robots, the robotsetting up and maintaining a coordination connection to these robots tocoordinate its motion path with the motion paths of the at least oneother robot for as long as its distance is less than the specifiedrelative distance, in which case one of the robots linked by thecoordination connection is selected as a coordinator and the other robotis selected as a partner, the coordinator requesting the plannedmovement segments of the partner and initiating an algorithm foravoiding collisions, with which the motion path segments of the partnerare harmonized with the motion path segments of the coordinator, inorder to determine the collision areas in which the robots are less thana specified minimum distance (d_(min)) apart and in which a timingsequence scheme for the motion path segments of the coordinator and thepartner is determined, the coordinator giving permission to itself andto the partner to execute the next motion path segment, on the basis ofthe timing sequence scheme for the motion path segments of thecoordinator and the partner, whereby the motion path segment is executedonly when the permission is granted, one of the robots initiating analgorithm to detect blocking in order to detect a group of mutuallyblocking robots if the detecting robot has not been granted permissionto execute its next motion path segment, on detection of a group ofmutually blocking robots by the detecting robot, the detecting robotinitiating an algorithm to resolve the blocking, whereby the resolvingalgorithm comprises at least a first step and optionally a second step,wherein, in the first step, the mutually blocking robots that areconnected by the coordination connection exchange the sequence forexecuting the next motion path segment, and in the second step, at leastone of the mutually blocking robots plan new motion paths, with thesecond step being executed only if the first step fails to resolve theblocking.
 2. The method according to claim 1, wherein the algorithm foravoiding collisions determines the time sequence scheme for the plannedmotion path segments of the coordinator and the partner by: presentingthe motion path segments of the coordinator and the partner inaccordance with a horizontal and a vertical axis of a two-dimensionaldiagram, checking for positions of the robots in the motion pathsegments that produce a distance for the robots that is less than aspecified minimum distance d_(min) and marking the positions ascollision areas, establishing an execution path that avoids all of themarked collision areas, beginning with a bottom left corner and endingin a top right corner of the two-dimensional diagram, dividing theexecution path into linear sections, beginning with the lower leftcorner of the diagram, and making an entry for each linear section inthe time sequence scheme, wherein for each horizontal section thecoordinator, for each vertical section the partner, and for eachdiagonal section both the coordinator and the partner are grantedpermission to execute the next motion path segment.
 3. The methodaccording to claim 2, wherein the execution path for the motion pathsegments is established to be as short as possible.
 4. The methodaccording to claim 3, wherein the execution path established hascollision paths that meet in the lowest left corner of the collisionareas.
 5. The method according to claim 1, wherein the algorithm todetect blocking includes: defining a directed coordination connectionsuch that the origin of a directed coordination connection is assignedto a waiting robot and the destination of the directed coordinationconnection is assigned to a priority robot, transmitting a test messagealong the newly defined directed coordination connection, receiving thetest message from the transmitting robot and forwarding the test messageto all of the receiving robot's outbound coordination connections, alongwith an identification of the robot forwarding the test message,receiving the forwarded test message from the forwarding robot andchecking as to whether the forwarded test message originated from therobot performing the checking, and detecting a mutual blocking situationwith a simultaneous identification of all robots, in the event of atleast one of: (i) the test message originates from one robot, and (ii)if the test message does not originate from the one robot, the testmessages are forwarded to all outbound coordination connections with theidentifications.
 6. The method according to claim 1, wherein the firststep of the algorithm to resolve the blocking includes: sending a changemessage to the group of the mutually blocking robots, receiving a changemessage by the robots involved in the group of mutually blocking robotsand inquiring of the coordinator as to whether the sequence forexecuting the next motion path segment is to be swapped, discarding thechange message if swapping the sequence of execution resolves theblocking, or receiving the change message by the robot initiating thechange message in order to initiate the second step, and whereby thesecond step of the algorithm to resolve the blocking includes: sending areplan message to the group of the mutually blocking robots, receivingthe replan message by the robots involved in the group of mutuallyblocking robots and requesting the robot planning the motion path toplan an alternate motion path, discarding the new plan message andremoving all directed coordination connections if an alternate motionpath is successfully planned by the robot, or receiving the new planmessage by the robot initiating the new plan message and thereuponinitiating a freeing message, sending the freeing message to the groupof mutually blocking robots, whereby the freeing message is enabled toleave the group, to cause all available robots to plan an alternatemotion path and to register whether a robot other than the mutuallyblocking robots is located in the vicinity of the mutually blockingrobots, receiving a freeing message by the robots initiating the freeingmessage, checking whether any of the mutually blocking robots can planan alternate motion path and whether any of the mutually blocking robotsregisters a non-blocking robot in its vicinity, and canceling theblocking resolution if an alternate motion path is planned or anon-blocking robot is registered.
 7. The method according to claim 1,wherein the mobile robots comprise robots configured to jointly clean anarea.
 8. The method according to claim 7, wherein the specifiedgeographical area comprises at least one of a supermarket and anairport.
 9. A method for automatic, decentralized coordination ofmovement paths between at least two mobile robots, which preventscollisions and detects and resolves mutual blocking situations betweenthe mobile robots, comprising: one of the robots receiving positioninformation from the other of the robots; establishing a coordinatingconnection between the one robot and the other robot if, according tothe position information, a position between the robots falls below apredetermined minimum acceptable distance; designating the two mobilerobots as respectively either a coordinator or a partner; wherein thecoordinator initiates a collision avoidance algorithm that utilizes atime sequence diagram for motion path segments of the coordinator andthe partner in order to prevent a collision between the one robot andthe other robot, and wherein the collision avoidance algorithm includesgranting authorization by the coordinator to execute a next step in themotion path segments to at least one of the coordinator and the partner;in the event of a failure by the collision avoidance algorithm tosuccessfully grant the authorization, initiating an algorithm fordetecting a mutual blocking situation; if the blocking detectionalgorithm detects a mutual blocking situation, initiating an algorithmfor resolving the blocking, including interchanging a sequence forexecuting the next step in the motion path between the coordinator andthe partner.
 10. The method according to claim 9, wherein, in the eventof a failure by the interchanging to successfully resolve the mutualblocking situation, the blocking resolution algorithm replans the motionpaths of the motion path segments of the time sequence diagram.